1. Field of the Invention
This invention relates to an apparatus for optically measuring the surface shape of the cornea of an eye to be examined.
2. Related Background Art
There is known an apparatus in which in order to measure the shape of a cornea, an index mark of a particular shape is projected onto the cornea, the reflected image from the surface of the cornea is passed through a measuring optical system to form a projected image including the shape of the cornea as information on the light receiving surface of a light receiving element and data obtained on the basis of the photoelectric output of the light receiving element is calculation-processed to thereby determine the surface shape of the cornea.
For example, U.S. Pat. No. 4,999,009 discloses an apparatus in which the index mark of a ring-shaped slit is projected onto the cornea of an eye to be examined. There is also known an apparatus in which concentric circular patterns are projected onto the cornea of an eye to be examined through a plurality of concentric circular slits and the surface shape of the cornea is measured on the basis of the analysis of the shapes of the reflected images thereof from the cornea.
However, for highly accurate measurement, it is necessary that more ring slit patterns differing in diameter can be projected onto the surface of the cornea, and the prior-art construction using concentric circular slits has had a limitation and has suffered from the problem that the apparatus becomes bulky.